1. Field of the Invention
The present invention relates to a dumbbell, and more particularly to a dumbbell having a handle portion attached to weight portions at positions deviating from the centers of gravity of the weight portions.
2. Description of the Background Art
Dumbbells made of iron, lead, etc., are known in the art for use in increasing the muscular power in the wrist, the shoulder, the arm, etc. A dumbbell includes a shaft, serving as a handle portion, and weights in a disc shape, a plate shape, a spherical shape, or the like, symmetrically attached at the opposite ends of the shaft. In order to increase the muscular power, one swings the dumbbell back and forth while gripping the shaft portion, with the shoulder, elbow, wrist, etc., serving as the fulcrum.
FIG. 24 is a view showing a wrist curl as an exercise example using a conventional dumbbell 90. The conventional dumbbell 90 includes weight portions 92 attached at the opposite ends of a handle portion 91. With an arm 94 resting on a bench 93, the dumbbell 90 is swung up and down with the wrist serving as the fulcrum. This increases the muscular power of the forearm.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2007-160041    Patent Document 2: Japanese Design Registration No. 1215761    Patent Document 3: Japanese Laid-Open Patent Publication No. 8-318006    Patent Document 4: Japanese Laid-Open Patent Publication No. 63-290587    Patent Document 5: Japanese Laid-Open Utility Model Publication No. 62-50661    Patent Document 6: Japanese National Phase PCT Laid-Open Publication No. 62-503075    Patent Document 7: Japanese Laid-Open Utility Model Publication No. 59-8360    Patent Document 8: Japanese Design Registration No. 1140495    Patent Document 9: Japanese Laid-Open Utility Model Publication No. 60-92555    Patent Document 10: Japanese Laid-Open Patent Publication No. 7-204292    Patent Document 11: Japanese Laid-Open Patent Publication No. 2004-255006    Patent Document 12: Japanese Laid-Open Patent Publication No. 11-216199    Patent Document 13: Japanese Design Registration No. 1183583    Patent Document 14: Japanese Laid-Open Utility Model Publication No. 60-102038